At one time there was no good way of cleaning sewers chemically. When cleaned mechanically as by rotary units or by similar devices, the roots tended to regrow until once again they reduced the passage area in the sewer, either closing the sewer off entirely, or at least reducing the flow through the sewer. During that period, copper sulfate was often recommended, but the trouble was that the copper sulfate acted only on the parts of the roots that were actually in the liquid along the bottom of the sewer, and sewers are purposely left to be mainly empty, not to be filled with liquid.
Radical improvements in the cleaning of sewers began with a new composition invented and introduced by Frederick F. Horne, and described in U.S. Pat. No. 3,741,807. Since that time some improvements have been made in foam-forming adjuvant. The present invention addresses problems which were not solved by the Horne or later inventions, and either solves them or substantially ameliorates the situation.
The composition shown in U.S. Pat. No. 3,741,807 consisted principally of three ingredients with an optional fourth one. The first ingredient was simply water which carried the active ingredients. The second ingredient was an alkaline metal alkyl dithiocarbamate, typically the one often called metham, and sold by Stauffer Chemical Co. in water solution under the trademark Vapam, Vapam being essentially a solution of about 37% metham and about 63% water. The third ingredient was a surfactant used in what would usually be considered gross quantities. The surfactant and the metham had to be compatible, and very few surfactants are compatible with metham. Moreover, as noted, the surfactant had to be in much greater quantity than where the surfactant was used merely as a wetting agent. The surfactant and the metham cooperated in a synergistic manner to do several things: (1) to maintain the active metham fumigant for a while in an active foam state on the pipe and root surfaces, (2) to provide, upon spraying or upon addition of air, a metham-surfactant foam, and to make that foam adhere well to all surfaces instead ineffectually running or dripping off the roots, (3) to remove coatings of slimes, greases, soaps, and dirt that have covered and protected the roots, and (4) to hold the metham fumigant on and near the cleaned root surfaces where the fumigant could be most effective. When attempts were made to use these ingredients separately they were not as successful, and the attempt to use the metham without large quantities of surfactant resulted in failure in instances where the roots were dirty or covered with slime or greases, such use without surfactant being successful only when the roots were at least relatively clean.
An added ingredient, often but not always used, was dichlobenil, which prevented rapid regrowth of the roots.
Although this composition has been very successful, there were factors that kept it from being as effective as would be desired, and it is these which are addressed by the present invention.
For one thing, the foam generated by the prior product was not sufficiently foamy to cling as persistently as would be hoped; it tended to drain away too quickly. Also, the foam was relatively unstable and of rather low density. The product also tended to result in a composition affording too low an expansion ratio to be sufficiently economical of its expensive constituents. Moreover, the concentrate tended to be unstable on long storage.
There were still other problems. One of these was that when hard water, especially water containing iron, was used to dilute the material, there tended to be a deleterious effect on the stability of the product.
The prior invention was such a great improvement over anything which the prior art had seen, that it has obtained wide use, but the present invention is a great improvement over that, and greatly improves overall efficiency.
The prior product was applied either (1) by moving a sprayer through the sewer, the spraying acting to produce a foam, (2) by soaking techniques, which though effective, tended to be rather wasteful of the material, and (3) by a later-developed foaming technique, using a pump that introduced air and water into the concentrate, and then conducting the foam itself directly into the sewer pipe, filling a certain length of it. In many ways this third technique was the best way to use the product, so far as amount of material required, but still there were difficulties due to the relatively low expansion ratio, the somewhat rapid drainage time, and the lack of sufficient clinging action of the foam to insure complete results.
The present invention therefore solves that problem by using--instead of a simple surfactant such as Triton X100, which was used generally in the previous product--a mixture of materials which when put together in the right proportion tends to produce optimum results and to solve the problems mentioned. The concentrate is then much more stable during storage, being much less sensitive to high heat or to freezing temperatures, and has good storage stability in the range of 33.degree. to 90.degree. F. It also produces a greatly improved foam which is denser, has a much larger expansion ratio, that is, can include much more air, is very slow to drain away and tends to cling to the roots very well. The present invention also gives improved foam stability, due to the discovery of the effect of pH on the stability of the product and use of the proper pH. The invention also provides improved release of the methyl isothiocyanate, which is the active ingredient coming from sodium methyl dithiocarbamate, or metham.